The 47-year-old, who is expected to return before the end of the year, was in the midst of implementing his strategic vision for the bank, which includes overseeing an EU-imposed sale of 632 branches, a revamp of its Halifax brand and around 15,000 job losses.

In a statement, Lloyds said: "The board of Lloyds Banking Group announces that following medical advice Antonio Horta-Osorio is taking a temporary leave of absence from his duties as group chief executive of the bank due to illness. Antonio is expected to return to his position before the end of the year."

Lloyds, which is 40.2% state-owned, said its board will meet later this morning to agree interim arrangements which will be announced in due course.

Shares in the bank fell 1.5% after Lloyds confirmed Mr Horta-Osorio's leave - but had already been under pressure amid increased uncertainty in the eurozone.

Group finance director Tim Tookey is understood to be lined up to stand in for Mr Horta-Osorio, however, Mr Tookey is leaving the company in February to join life assurer Friends Life.

Mr Horta-Osorio, who was absent from a parliamentary committee meeting on Tuesday, takes leave less than a week before the banking giant is due to reveal its third-quarter results.

Lloyds reported a £3.3 billion pre-tax loss in the six months to June, compared with a £1.3 billion profit last year, as the cost of the payment protection insurance (PPI) scandal took its toll.

Stripping out the provision set aside for customers mis-sold PPI, the bank saw underlying profits plunge 31% to £1.1 billion as it struggled with the "subdued" economic climate.